1. Field of the Invention
The present invention relates to an image reading apparatus for especially reading a color original image and an image reading system using the same.
2. Related Background Art
FIG. 13 is a sectional view showing an example of an image sensor. This sensor is constituted by a sensor array 1 which is prepared by mounting a sensor IC 101 on a sensor board 102, a lens array 2, an LED array 6 having three different LED elements 301, 302, and 303 serving as light sources for illuminating an original, a cover glass 4, and a frame 5 for holding these components in position.
The LED array 6 is constituted by mounting, on the board, a plurality of three different types of LED elements 301, 302, and 303, for example, 20 or more elements on each line to obtain a uniform illuminance distribution of an original upon reading an A4-size original.
The emission peak wavelengths of the three different LED elements 301, 302, and 303 are respectively 430 (nm) corresponding to blue, 570 (nm) corresponding to green, and 660 (nm) corresponding to red.
The lens array 2 is formed by arranging a plurality of columnar lens elements on a line to provide a lens function by setting gradually different refractive indices between the peripheral portion and the central portion.
Also, as the lens array 2, one having a small aperture angle is selected angle since some color originals are adhered with pictures and have three-dimensional patterns on their surface and, hence, a focal length of about 0.5 (mm) is required. Furthermore, a lens array 2 having small chromatic aberrations is selected so that R, G, and B light beams can obtain substantially equal resolutions on the corresponding sensors.
In general, a lens array having an aperture angle of about 12 (deg.) is used, and a conjugate length (TC) as the distance between the original and sensor requires 18.3 (mm).
However, since the above-mentioned conventional image sensor uses a lens array with a small aperture angle, the light amount transmission efficiency is low, and an increase in original reading speed is limited.
In addition, in the lens array having a small aperture angle, distance from the original surface to the sensor is large, so that the size of the image sensor using such the lens array becomes large.
Furthermore, in the above-mentioned conventional image sensor, since the lens array equally inputs R, G, and B light beams onto the sensor array, a moire phenomenon appears, i.e., a very thin line in the read original is output as a shaggy line in the output image. Such phenomenon is especially conspicuous in a color original output image.
It is an object of the present invention to provide an image reading apparatus and system, which can complete reading within a short period of time.
It is another object of the present invention to provide a compact, inexpensive image reading apparatus and system.
It is still another object of the present invention to eliminate production of moire noise upon reading a color image.
In order to achieve the above objects, according to one embodiment of the present invention, an image reading apparatus comprises: a photoelectric conversion element; an illumination device having light sources of first, second, and third colors having longer emission wavelengths in the order named; an imaging member for imaging light reflected by an original illuminated by the illumination device onto the photoelectric conversion element; and a support member for supporting the original, wherein an optical distance from a center of the imaging member to the photoelectric conversion element is set at xc2xd of a conjugate length of light having a wavelength longer than a peak value of the emission wavelength of the light source of the second color, and an optical distance from the center of the imaging member to a surface of the original supported by the support member is set at xc2xd of a conjugate length of light of the emission wavelength having a conjugate length shorter than the conjugate length.
According to another embodiment of the present invention, an image reading system comprises: a photoelectric conversion element; an illumination device having light sources of first, second, and third colors having longer emission wavelengths in the order named; an imaging member for imaging light reflected by an original illuminated by the illumination device onto the photoelectric conversion element; a support member for supporting the original; and control means for controlling the photoelectric conversion element and the illumination device, wherein an optical distance from a center of the imaging member to the photoelectric conversion element is set at xc2xd of a conjugate length of light having a wavelength longer than a peak value of the emission wavelength of the light source of the second color, and an optical distance from the center of the imaging member to a surface of the original supported by the support member is set at xc2xd of a conjugate length of light of the emission wavelength having a conjugate length shorter than the conjugate length.
According to still another embodiment of the present invention, an image reading apparatus comprises: a photoelectric conversion element; an illumination device having light sources of first, second, and third colors having longer emission wavelengths in the order named; an imaging member for imaging light reflected by an original illuminated by the illumination device onto the photoelectric conversion element; and a support member for supporting the original, wherein an optical distance from a center of the imaging member to the photoelectric conversion element is set at xc2xd of a conjugate length at the emission wavelength of the light source of the third color, and an optical distance from the center of the imaging member to a surface of the original supported by the support member is set at xc2xd of a conjugate length at the emission wavelength of the light source of the second color.
According to still another embodiment of the present invention, an image reading system comprises: a photoelectric conversion element; an illumination device having light sources of first, second, and third colors having longer emission wavelengths in the order named; an imaging member for imaging light reflected by an original illuminated by the illumination device onto the photoelectric conversion element; a support member for supporting the original; and control means for controlling the photoelectric conversion element and the illumination device, wherein an optical distance from a center of the imaging member to the photoelectric conversion element is set at xc2xd of a conjugate length at the emission wavelength of the light source of the third color, and an optical distance from the center of the imaging member to a surface of the original supported by the support member is set at xc2xd of a conjugate length at the emission wavelength of the light source of the second color.
With the above arrangement, the reading time can be shortened while realizing size and cost reductions of the reading apparatus and system.
According to still another embodiment of the present invention, an image reading apparatus comprises: a photoelectric conversion element; an illumination device having light sources of first, second, and third colors having longer emission wavelengths in the order named; and an imaging member for imaging light reflected by an original illuminated by the illumination device onto the photoelectric conversion element, wherein a conjugate length TC of the imaging member is set to satisfy Axe2x89xa6TCxe2x89xa6B where A is the conjugate length at the emission wavelength of the light source of the second color, and B is the conjugate length at the emission wavelength of the light source of the third color.
According to still another embodiment of the present invention, an image reading system comprises: a photoelectric conversion element; an illumination device having light sources of first, second, and third colors having longer emission wavelengths in the order named; an imaging member for imaging light reflected by an original illuminated by the illumination device onto the photoelectric conversion element; and control means for controlling the photoelectric conversion element and the illumination device, wherein a conjugate length TC of the imaging member is set to satisfy Axe2x89xa6TCxe2x89xa6B where A is the conjugate length at the emission wavelength of the light source of the second color, and B is the conjugate length at the emission wavelength of the light source of the third color.
With the above-mentioned arrangement, a compact, inexpensive image reading apparatus and system can be provided, and production of moire upon reading a color image can be eliminated.